A load control device may control the amount of power delivered to an electrical load. Load control devices include, for example, lighting control devices (such as wall-mounted dimmer switches and plug-in lamp dimmers), motor control devices (for motor loads), temperature control devices, motorized window treatments, and remote controls. FIG. 1A is an exemplary environment 10 that may utilize a number of load control devices. In FIG. 1A, the illustrated load control devices may control lighting loads 12, smart thermostats 14, and/or motorized window treatments 16 in a typical (household) environment. Typically, a load control device, such as a dimmer switch, may be coupled in a series electrical connection between an alternating-current (AC) power source and the electrical load, such as one of the lighting loads 12, to control the power delivered from the AC power source to the electrical load.
Some load control devices are operable to transmit and receive wireless signals, such as radio-frequency (RF) or infrared (IR) signals, to thus provide for wireless control of the corresponding loads. One example of an RF lighting control system is disclosed in commonly-assigned U.S. Pat. No. 5,905,442, issued May 18, 1999, entitled METHOD AND APPARATUS FOR CONTROLLING AND DETERMINING THE STATUS OF ELECTRICAL DEVICES FROM REMOTE LOCATIONS, the entire disclosure of which is hereby incorporated by reference.
Wi-Fi technology (e.g., the 802.11 family of wireless technologies) is an example technology that may be used with RF wireless communication systems, such as load control systems for controlling load control devices and electrical loads. Examples of Wi-Fi-enabled load control devices include those described in commonly-assigned U.S. application Ser. No. 13/538,555, filed Jun. 29, 2012, titled LOAD CONTROL DEVICE HAVING INTERNET CONNECTIVITY, the contents of which is hereby incorporated by reference herein in its entirety, for all purposes.
Wi-Fi technology may be used in a contention-based shared network in which the wireless resources are shared among the users—each vying for the opportunity to transmit and receive information on a common channel. This competition can cause variation in communication latency, where certain transmissions are made with relatively low latency and other transmissions may have to wait much longer before the channel is available for transmission. This variation in latency is particularly problematic when communicating commands to load control devices.
To illustrate, as shown in FIGS. 1B and 1C, a room in a house may have four different lighting loads, e.g., a floor lamp 20, a table lamp 22, a sconce 24, and recessed ceiling lights 26. Each lighting load may be controlled by a different load control device. When wireless commands are sent to each device with varying latency, each device may execute those commands at different times. And, rather than all of the lights pleasantly coming on or off together, as shown in FIG. 1B, there is an unpleasant randomness to the lights coming on or off at different times, as shown in FIG. 1C. Here, the recessed ceiling lights 26 are the first to respond, then the sconce 24 and table lamp 22, followed by the floor lamp 20. This unfortunate problem may be known as the “pop-corn” effect, and it is an undesirable aesthetic for the operation of the system.
Wi-Fi-enabled devices may communicate using a carrier-service multiple access (CSMA) communication protocol. CSMA protocols often experience multi-path issues, propagation delays, and the burdens of a shared protocol (e.g., having to accommodate IP packets for a large number of devices, including transient devices, that introduce IP packets at various and unpredictable times). For example, devices that may use CSMA protocols verify the absence of other traffic before transmitting on the shared transmission medium. Because of such issues that may be encountered with Wi-Fi technology, among other reasons, when a user commands a dimming action of the floor lamp 20, the table lamp 22, the sconce 24, and the ceiling lights 26 (e.g. via Wi-Fi transmitted commands to respective dimmer switches that may control those lighting loads)—the user may observe the popcorn effect. For example, a dimmer switch for the floor lamp 20 may turn on the floor lamp 20 one or more seconds before a dimmer switch for the floor lamp 22 may turn on the floor lamp 22—which may occur one or more seconds before a dimmer switch for the sconce 24 may turn on the sconce 24.
The wireless system would have an increased benefit from the ability to leverage wireless networks with varying latency (such as contention-based shared wireless technologies, like Wi-Fi technology for example) if the pop-corn effect could be mitigated and/or eliminated.